In frame switched communication networks, information is forwarded from a source to a destination based in whole or part on a destination address. In Bridged Ethernet communication networks these addresses are called Media Access Control (MAC) addresses. MAC addresses identify the source and destination station (end or intermediate, individual or group) of each frame, however typically don't contain any subfields which identify the physical or logical location (or subnetworks) of the station. Such an address can be called a flat address.
Recent advances in Bridged Ethernet frame switched communication networks have eliminated the limitations of both geographic size and number of supported nodes. Specifically, Provider Backbone Bridging (IEEE 802.1ah) along with the supporting control plane (IEEE draft 802.1aq) allows a single Bridged Ethernet to span any distance and to support as many nodes as can be addressed by MAC addresses.
Within a very large Bridged Ethernet each Bridge must hold a table of most of the MAC addresses forwarded by that Bridge. Since the size of these MAC address tables grows in proportion to the number of Ethernet MAC addresses passing through each Bridge these tables constrain the practical network size.
Further, Ethernet Bridges don't have methods for aggregating MAC addresses or for forwarding frames based on aggregates rather than the individual or group station MAC addresses. The use of non-aggregated flat individual or group station MAC addresses for frame forwarding limits the scaling, lowers the efficiency, reduces the security and raises the cost of these networks.